LTC3588-2 Nanopower Energy Harvesting Power Supply with 14V Minimum VIN DESCRIPTION FEATURES 1500nA Input Quiescent Current (Output in Regulation – No Load, VIN = 18V) nn 830nA Input Quiescent Current in UVLO, V = 12V IN nn 14V to 20V Input Operating Range nn Integrated Low-Loss Full-Wave Bridge Rectifier nn 16V UVLO Improves Power Utilization from High Voltage Current Limited Inputs nn Up to 100mA of Output Current nn High Efficiency Integrated Hysteretic Buck DC/DC nn Selectable Output Voltages: 3.45V, 4.1V, 4.5V, 5.0V nn Input Protective Shunt – Up to 25mA Pull-Down at VIN ≥ 20V nn Available in 10-Lead MSE and 3mm × 3mm DFN Packages The LTC®3588-2 integrates a low-loss full-wave bridge rectifier with a high efficiency buck converter to form a complete energy harvesting solution optimized for high output impedance energy sources such as piezoelectric, solar, or magnetic transducers. APPLICATIONS Four output voltages of 3.45V, 4.1V, 4.5V and 5.0V are pin selectable with up to 100mA of continuous output current, and suit Li-Ion and LiFePO4 batteries as well as supercapacitors. An input protective shunt set at 20V provides overvoltage protection. nn Piezoelectric Energy Harvesting Electro-Mechanical Energy Harvesting nn Low Power Battery Charging nn Wireless HVAC Sensors nn Mobile Asset Tracking nn Tire Pressure Sensors nn Battery Replacement for Industrial Sensors nn nn An ultralow quiescent current undervoltage lockout (UVLO) mode with a 16V rising threshold enables efficient energy extraction from sources with high open circuit voltages. This energy is transferred from the input capacitor to the output via a high efficiency synchronous buck regulator. The 16V UVLO threshold also allows for input to output current multiplication through the buck regulator. The buck features a sleep state that minimizes both input and output quiescent currents while in regulation. L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION High Voltage Piezoelectric Energy Harvesting Power Supply LTC3588-2 5.0V Regulator Start-Up Profile 20 CIN = 10µF, CSTORAGE = 47µF 18 NO LOAD, IVIN = 2µA 16 MIDE V25W 1µF 6V 10µF 25V 4.7µF 6V VIN PZ2 LTC3588-2 SW VOUT CSTORAGE 6V VOUT CAP PGOOD VIN2 D0, D1 GND 35882 TA01 14 22µH 2 OUTPUT VOLTAGE SELECT VOLTAGE (V) PZ1 VIN 12 10 8 VOUT 6 4 2 0 PGOOD = LOGIC 1 0 400 200 600 TIME (sec) 35882 TA01b 35882fc For more information www.linear.com/LTC3588-2 1 LTC3588-2 ABSOLUTE MAXIMUM RATINGS (Note 1) VIN Low Impedance Source........................ –0.3V to 18V* Current Fed, ISW = 0A....................................... 25mA† PZ1, PZ2............................................................0V to VIN D0, D1...............–0.3V to [Lesser of (VIN2 + 0.3V) or 6V] CAP....................... [Higher of –0.3V or (VIN – 6V)] to VIN VIN2.................... –0.3V to [Lesser of (VIN + 0.3V) or 6V] * VIN has an internal 20V clamp † For t < 1ms and Duty Cycle < 1%, Absolute Maximum Continuous Current = 5mA VOUT................... –0.3V to [Lesser of (VIN + 0.3V) or 6V] PGOOD.............–0.3V to [Lesser of (VOUT + 0.3V) or 6V] IPZ1, IPZ2.............................................................. ±50mA ISW....................................................................... 350mA Operating Junction Temperature Range (Notes 2, 3)................................................. –40 to 125°C Storage Temperature Range....................... –65 to 125°C Lead Temperature (Soldering, 10 sec) MSE Only........................................................... 300°C PIN CONFIGURATION TOP VIEW PZ1 1 PZ2 2 CAP 3 VIN 4 SW 5 TOP VIEW 10 PGOOD 11 GND PZ1 PZ2 CAP VIN SW 9 D0 8 D1 7 VIN2 6 VOUT 1 2 3 4 5 11 GND 10 9 8 7 6 PGOOD D0 D1 VIN2 VOUT MSE PACKAGE 10-LEAD PLASTIC MSOP DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W, θJC = 7.5°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB TJMAX = 125°C, θJA = 45°C/W, θJC = 10°C/W EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3588EDD-2#PBF LTC3588EDD-2#TRPBF LFYK 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LTC3588IDD-2#PBF LTC3588IDD-2#TRPBF LFYK 10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C LTC3588EMSE-2#PBF LTC3588EMSE-2#TRPBF LTFYM 10-Lead Plastic MSOP –40°C to 125°C LTC3588IMSE-2#PBF LTC3588IMSE-2#TRPBF LTFYM 10-Lead Plastic MSOP –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ This product is only offered in trays. For more information go to: http://www.linear.com/packaging/ 2 35882fc For more information www.linear.com/LTC3588-2 LTC3588-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VIN = 18V unless otherwise specified. SYMBOL PARAMETER CONDITIONS VIN Input Voltage Range Low Impedance Source on VIN IQ VIN Quiescent Current UVLO Buck Enabled, Sleeping Buck Enabled, Not Sleeping VIN = 12V, Not PGOOD VIN = 18V ISW = 0A (Note 4) VUVLO VIN Undervoltage Lockout Threshold VIN Rising l VIN Falling l VSHUNT VIN Shunt Regulator Voltage IVIN = 1mA ISHUNT Maximum Protective Shunt Current 1ms Duration 25 Internal Bridge Rectifier Loss (|VPZ1 – VPZ2| – VIN) IBRIDGE = 10µA 350 Internal Bridge Rectifier Reverse Leakage Current VREVERSE = 18V Internal Bridge Rectifier Reverse Breakdown Voltage IREVERSE = 1µA Regulated Output Voltage 3.45V Output Selected Sleep Threshold Wake-Up Threshold 4.1V Output Selected Sleep Threshold Wake-Up Threshold 4.5V Output Selected Sleep Threshold Wake-Up Threshold 5.0V Output Selected Sleep Threshold Wake-Up Threshold VOUT MIN MAX UNITS 18.0 V 830 1500 150 1400 2500 250 nA nA µA 16.0 17.0 V 13.0 14.0 18.8 20.0 V 21.2 V mA 400 450 mV 20 nA VSHUNT 30 l l 3.346 3.466 3.434 3.554 V V l l 3.979 4.116 4.084 4.221 V V l l 4.354 4.516 4.484 4.646 V V l l 4.825 5.016 4.984 5.175 V V 125 250 nA 260 350 mA PGOOD Falling Threshold As a Percentage of the Selected VOUT IVOUT Output Quiescent Current VOUT = 5.0V IPEAK Buck Peak Switch Current 200 IBUCK Available Buck Output Current 100 RP Buck PMOS Switch On-Resistance RN TYP l 83 V 92 % mA 1.1 Buck NMOS Switch On-Resistance Ω 1.3 Ω Max Buck Duty Cycle l 100 % VIH(D0, D1) D0/D1 Input High Voltage l 1.2 V VIL(D0, D1) D0/D1 Input Low Voltage l IIH(D0, D1) IIL(D0, D1) 0.4 V D0/D1 Input High Current 10 nA D0/D1 Input Low Current 10 nA Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3588E-2 is tested under pulsed load conditions such that TJ ≈ TA. The LTC3588E-2 is guaranteed to meet specifications from 0°C to 85°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3588I-2 is guaranteed over the –40°C to 125°C operating junction temperature range. Note that the maximum ambient temperature consistent with these specifications is determined by specific operating conditions in conjunction with board layout, the rated package thermal impedance and other environmental factors. Note 3: The junction temperature (TJ, in °C) is calculated from the ambient temperature (TA, in °C) and power dissipation (PD, in Watts) according to the formula: TJ = TA + (PD • θJA), where θJA (in °C/W) is the package thermal impedance. Note 4: Dynamic supply current is higher due to gate charge being delivered at the switching frequency. 35882fc For more information www.linear.com/LTC3588-2 3 LTC3588-2 TYPICAL PERFORMANCE CHARACTERISTICS Input IQ in UVLO vs VIN 125°C 1600 125°C 16.2 2800 1200 85°C 1000 INPUT IQ (nA) INPUT IQ (nA) UVLO Rising vs Temperature 16.4 3200 1400 25°C 800 –40°C 600 400 200 0 Input IQ in Sleep vs VIN 3600 0 2 4 6 8 10 VIN (V) 12 14 UVLO RISING (V) 1800 2400 2000 85°C 1600 25°C 1200 –40°C 800 16 14 15 16 VIN (V) 35882 G01 UVLO Falling vs Temperature 15.8 15.6 –50 18 17 21.2 1800 21.0 1600 VBRIDGE (mV) VSHUNT (V) UVLO FALLING (V) ISHUNT = 25mA 20.0 ISHUNT = 1mA 19.8 19.6 13.8 19.4 0 25 75 50 TEMPERATURE (°C) 100 18.8 –50 125 –25 35882 G04 800 100 0 125 1.6 14 1.4 12 1.2 3.50 1.0 0.8 3.30 3.25 3.20 2 0.2 3.15 35882 G07 WAKE-UP THRESHOLD 3.35 0.4 0 SLEEP THRESHOLD 3.40 4 170 10m 3.45 0.6 35 80 125 TEMPERATURE (°C) 100µ 1m BRIDGE CURRENT (A) 3.45V Output vs Temperature 6 –10 10µ 3.55 VOUT (V) 16 8 1µ 35882 G06 4VP-P APPLIED TO PZ1/PZ2 INPUT 1.8 MEASURED IN UVLO 10 25°C 600 Bridge Frequency Response VIN = 18V, LEAKAGE AT PZ1 OR PZ2 0 –55 4 0 25 75 50 TEMPERATURE (°C) 2.0 VIN (V) BRIDGE LEAKAGE (nA) 18 85°C 35882 G05 Bridge Leakage vs Temperature 20 1000 200 19.0 –25 –40°C 1200 400 19.2 13.6 –50 |VPZ1 – VPZ2| – VIN 1400 20.4 20.2 125 Total Bridge Rectifier Drop vs Bridge Current 20.6 14.0 100 35882 G03 20.8 14.2 0 25 75 50 TEMPERATURE (°C) –25 35882 G02 VSHUNT vs Temperature 14.4 16.0 10 100 1k 10k 100k 1M FREQUENCY (Hz) 10M 100M 35882 G08 3.10 –50 PGOOD FALLING –25 0 25 75 50 TEMPERATURE (°C) 100 125 35882 G09 35882fc For more information www.linear.com/LTC3588-2 LTC3588-2 TYPICAL PERFORMANCE CHARACTERISTICS 4.1V Output vs Temperature 4.60 5.10 SLEEP THRESHOLD SLEEP THRESHOLD SLEEP THRESHOLD 4.10 5.00 4.50 WAKE-UP THRESHOLD WAKE-UP THRESHOLD WAKE-UP THRESHOLD 3.90 4.90 4.40 VOUT (V) 4.00 VOUT (V) VOUT (V) 5.0V Output vs Temperature 4.5V Output vs Temperature 4.20 4.30 4.80 4.70 3.80 4.20 PGOOD FALLING 3.70 –50 –25 0 25 75 50 TEMPERATURE (°C) 100 4.10 –50 125 0 25 75 50 TEMPERATURE (°C) –25 35882 G10 IVOUT (nA) VOUT (V) 4.10 4.09 VOUT = 4.1V 14 15 35882 G13 300 16 VIN (V) 17 260 RDS(ON) (Ω) IPEAK (mA) 1.6 250 240 220 NMOS SWITCH VOLTAGE 10V/DIV 1.4 PMOS 0V INDUCTOR CURRENT 200mA/DIV 1.0 210 –25 0 75 25 50 TEMPERATURE (°C) 100 125 35882 G16 0.8 –55 –35 –15 125 35882 G15 1.2 230 100 OUTPUT VOLTAGE 50mV/DIV AC-COUPLED 1.8 270 0 75 25 50 TEMPERATURE (°C) Operating Waveforms 2.0 280 –25 35882 G14 290 200 –50 40 –50 18 RDS(ON) of PMOS/NMOS vs Temperature IPEAK vs Temperature VOUT = 3.45V 60 4.06 4.05 100 80 4.07 100m VOUT = 4.5V 120 4.11 4.08 4.05 125 VOUT = 5.0V 140 4.12 100µ 1m 10m LOAD CURRENT (A) 100 IVOUT vs Temperature 4.13 10µ 50 0 25 75 TEMPERATURE (°C) 160 COUT = 100µF, ILOAD = 60mA, 4.14 D1 = 0, D0 = 1 VIN = 18V, COUT = 100µF, D1 = 0, D0 = 1 1µ –25 35882 G12 VOUT Line Regulation 4.10 4.00 4.50 –50 125 4.15 4.15 VOUT (V) 100 35882 G11 VOUT Load Regulation 4.20 PGOOD FALLING 4.60 PGOOD FALLING 0mA 5 25 45 65 85 105 125 TEMPERATURE (°C) 35882 G17 2.5µs/DIV VIN = 18V, VOUT = 5.0V ILOAD = 1mA L = 22µH, COUT = 47µF 35882 G18 35882fc For more information www.linear.com/LTC3588-2 5 LTC3588-2 TYPICAL PERFORMANCE CHARACTERISTICS 100 94 VIN = 15V 90 80 EFFICIENCY (%) EFFICIENCY (%) 70 60 50 40 30 10 0 1µ 10µ 100µ 1m 10m LOAD CURRENT (A) 90 90 80 88 86 80 14 15 35881 G19 90 94 VIN = 15V 70 EFFICIENCY (%) EFFICIENCY (%) 80 60 50 40 30 VOUT = 5.0V VOUT = 4.5V VOUT = 4.1V VOUT = 3.45V 20 10 0 1µ 10µ 100µ 1m 10m LOAD CURRENT (A) 100m 35882 G22 6 17 70 60 30 18 100 92 90 90 80 88 86 VOUT = 5.0V VOUT = 4.5V VOUT = 4.1V VOUT = 3.45V 82 80 14 15 16 VIN (V) 14 15 35882 G20 Efficiency vs VIN for ILOAD = 100mA, L = 100µH 84 ILOAD = 100mA ILOAD = 100µA ILOAD = 50µA ILOAD = 30µA ILOAD = 10µA 40 EFFICIENCY (%) 100 Efficiency vs ILOAD, L = 100µH 16 VIN (V) Efficiency vs VIN for VOUT = 4.1V, L = 22µH 50 VOUT = 5.0V VOUT = 4.5V VOUT = 4.1V VOUT = 3.45V 82 100m 100 92 84 VOUT = 5.0V VOUT = 4.5V VOUT = 4.1V VOUT = 3.45V 20 Efficiency vs VIN for ILOAD = 100mA, L = 22µH EFFICIENCY (%) Efficiency vs ILOAD, L = 22µH 17 18 35882 G23 16 VIN (V) 17 18 35882 G21 Efficiency vs VIN for VOUT = 4.1V, L = 100µH 70 60 ILOAD = 100mA ILOAD = 100µA ILOAD = 50µA ILOAD = 30µA ILOAD = 10µA 50 40 30 14 15 16 VIN (V) 17 18 35882 G24 35882fc For more information www.linear.com/LTC3588-2 LTC3588-2 PIN FUNCTIONS PZ1 (Pin 1): Input connection for piezoelectric element or other AC source (used in conjunction with PZ2). VIN2 (Pin 7): Internal low voltage rail to serve as gate drive for buck NMOS switch. Also serves as a logic high rail for output voltage select bits D0 and D1. A 4.7µF capacitor should be connected from VIN2 to GND. This pin is not intended for use as an external system rail. PZ2 (Pin 2): Input connection for piezoelectric element or other AC source (used in conjunction with PZ1). CAP (Pin 3): Internal rail referenced to VIN to serve as gate drive for buck PMOS switch. A 1µF capacitor should be connected between CAP and VIN. This pin is not intended for use as an external system rail. D1 (Pin 8): Output Voltage Select Bit. D1 should be tied high to VIN2 or low to GND to select desired VOUT (see Table 1). D0 (Pin 9): Output Voltage Select Bit. D0 should be tied high to VIN2 or low to GND to select desired VOUT (see Table 1). VIN (Pin 4): Rectified Input Voltage. A capacitor on this pin serves as an energy reservoir and input supply for the buck regulator. The VIN voltage is internally clamped to a maximum of 20V (typical). PGOOD (Pin 10): Power good output is logic high when VOUT is above 92% of the target value. The logic high is referenced to the VOUT rail. SW (Pin 5): Switch Pin for the Buck Switching Regulator. A 22µH or larger inductor should be connected from SW to VOUT. GND (Exposed Pad Pin 11): Ground. The Exposed Pad should be connected to a continuous ground plane on the second layer of the printed circuit board by several vias directly under the LTC3588-2. VOUT (Pin 6): Sense pin used to monitor the output voltage and adjust it through internal feedback. BLOCK DIAGRAM VIN 4 20V INTERNAL RAIL GENERATION PZ1 1 3 CAP 5 SW 7 VIN2 PZ2 2 BUCK CONTROL UVLO 11 GND SLEEP BANDGAP REFERENCE 8, 9 D1, D0 6 VOUT 2 PGOOD COMPARATOR 10 PGOOD 35882 BD 35882fc For more information www.linear.com/LTC3588-2 7 LTC3588-2 OPERATION Internal Bridge Rectifier The LTC3588-2 has an internal full-wave bridge rectifier accessible via the differential PZ1 and PZ2 inputs that rectifies AC inputs such as those from a piezoelectric element. The rectified output is stored on a capacitor at the VIN pin and can be used as an energy reservoir for the buck converter. The low-loss bridge rectifier has a total drop of about 400mV with typical piezo generated currents (~10µA). The bridge is capable of carrying up to 50mA. One side of the bridge can be operated as a single-ended DC input. PZ1 and PZ2 should never be shorted together when the bridge is in use. Undervoltage Lockout (UVLO) When the voltage on VIN rises above the UVLO rising threshold the buck converter is enabled and charge is transferred from the input capacitor to the output capacitor. A wide (~2V) UVLO hysteresis window allows a portion of the energy stored on the input capacitor to be transferred to the output capacitor by the buck. When the input capacitor voltage is depleted below the UVLO falling threshold the buck converter is disabled. Extremely low quiescent current (830nA typical, VIN = 12V) in UVLO allows energy to accumulate on the input capacitor in situations where energy must be harvested from low power sources. Internal Rail Generation Two internal rails, CAP and VIN2, are generated from VIN and are used to drive the high side PMOS and low side NMOS of the buck converter, respectively. Additionally the VIN2 rail serves as logic high for output voltage select bits D0 and D1. The VIN2 rail is regulated at 4.8V above GND while the CAP rail is regulated at 4.8V below VIN. These are not intended to be used as external rails. Bypass capacitors 8 are connected to the CAP and VIN2 pins to serve as energy reservoirs for driving the buck switches. When VIN is below 4.8V, VIN2 is equal to VIN and CAP is held at GND. Figure 1 shows the ideal VIN, VIN2 and CAP relationship. 18 16 14 VOLTAGE (V) The LTC3588-2 is an ultralow quiescent current power supply designed specifically for energy harvesting and/or low current step-down applications. The part is designed to interface directly to a piezoelectric or alternative A/C power source, rectify a voltage waveform and store harvested energy on an external capacitor, bleed off any excess power via an internal shunt regulator, and maintain a regulated output voltage by means of a nanopower high efficiency synchronous buck regulator. VIN 12 10 8 6 VIN2 4 CAP 2 0 0 5 10 VIN (V) 15 35882 F01 Figure 1. Ideal VIN, VIN2 and CAP Relationship Buck Operation The buck regulator uses a hysteretic voltage algorithm to control the output through internal feedback from the VOUT sense pin. The buck converter charges an output capacitor through an inductor to a value slightly higher than the regulation point. It does this by ramping the inductor current up to 260mA through an internal PMOS switch and then ramping it down to 0mA through an internal NMOS switch. This efficiently delivers energy to the output capacitor. The ramp rate is determined by VIN, VOUT, and the inductor value. If the input voltage falls below the UVLO falling threshold before the output voltage reaches regulation, the buck converter will shut off and will not be turned on until the input voltage again rises above the UVLO rising threshold. During this time the output voltage will be loaded by approximately 100nA. When the buck brings the output voltage into regulation the converter enters a low quiescent current sleep state that monitors the output voltage with a sleep comparator. During this operating mode load current is provided by the buck output capacitor. When the output voltage falls below the regulation point the buck regulator wakes up and the cycle repeats. This hysteretic method of providing a regulated output reduces losses associated with FET switching and maintains an output at light loads. The buck delivers a minimum of 100mA of average current to the output when it is switching. For more information www.linear.com/LTC3588-2 35882fc LTC3588-2 OPERATION Though the quiescent current when the buck is switching is much greater than the sleep quiescent current, it is still a small percentage of the average inductor current which results in high efficiency over most load conditions. The buck operates only when sufficient energy has been accumulated in the input capacitor and the length of time the converter needs to transfer energy to the output is much less than the time it takes to accumulate energy. Thus, the buck operating quiescent current is averaged over a long period of time so that the total average quiescent current is low. This feature accommodates sources that harvest small amounts of ambient energy. regulation voltage. Several sleep cycles may occur during this time. Additionally, if PGOOD is high and VIN falls below the UVLO falling threshold, PGOOD will remain high until VOUT falls to 92% of the desired regulation point. This allows output energy to be used even if the input is lost. Figure 2 shows the behavior for VOUT = 5V and a 10µA load. At t = 2s VIN becomes high impedance and is discharged by the quiescent current of the LTC3588-2 and through servicing VOUT which is discharged by its own leakage current. VIN crosses UVLO falling but PGOOD remains high until VOUT decreases to 92% of the desired regulation point. The PGOOD pin is designed to drive a microprocessor or other chip I/O and is not intended to drive higher current loads such as an LED. The D0/D1 inputs can be switched while in regulation as shown in Figure 3. If VOUT is programmed to a voltage with a PGOOD falling threshold above the old VOUT, PGOOD will 20 18 12 C = 10µF, IN 10 COUT = 47µF, ILOAD = 10µA 8 6 2 0 VOUT VOUT QUIESCENT CURRENT (IVOUT) 0 3.45V 86nA 0 1 4.1V 101nA 1 0 4.5V 111nA 1 1 5.0V 125nA The internal feedback network draws a small amount of current from VOUT as listed in Table 1. Power Good Comparator A power good comparator produces a logic high referenced to VOUT on the PGOOD pin the first time the converter reaches the sleep threshold of the programmed VOUT, signaling that the output is in regulation. The PGOOD pin will remain high until VOUT falls to 92% of the desired PGOOD 0 2 4 6 8 TIME (sec) 12 10 35882 F02 Figure 2. PGOOD Operation During Transition to UVLO 6 COUT = 100µF, ILOAD = 100mA D1=D0=1 D1=D0=0 5 VOUT VOLTAGE (V) D0 VOUT 4 Table 1. Output Voltage Selection 0 VIN = UVLO FALLING 14 Four selectable voltages are available by tying the output select bits, D0 and D1, to GND or VIN2. Table 1 shows the four D0/D1 codes and their corresponding output voltages. D1 VIN 16 VOLTAGE (V) When the sleep comparator signals that the output has reached the sleep threshold the buck converter may be in the middle of a cycle with current still flowing through the inductor. Normally both synchronous switches would turn off and the current in the inductor would freewheel to zero through the NMOS body diode. The LTC3588-2 keeps the NMOS switch on during this time to prevent the conduction loss that would occur in the diode if the NMOS were off. If the PMOS is on when the sleep comparator trips the NMOS will turn on immediately in order to ramp down the current. If the NMOS is on it will be kept on until the current reaches zero. 4 D1=D0=0 VOUT 3 2 PGOOD = LOGIC 1 1 0 0 2 4 6 8 10 12 14 16 18 20 TIME (ms) 35882 F03 Figure 3. PGOOD Operation During D0/D1 Transition 35882fc For more information www.linear.com/LTC3588-2 9 LTC3588-2 OPERATION transition low until the new regulation point is reached. When VOUT is programmed to a lower voltage, PGOOD will remain high through the transition. Energy Storage Harvested energy can be stored on the input capacitor or the output capacitor. The high UVLO threshold takes advantage of the fact that energy storage on a capacitor is proportional to the square of the capacitor voltage. After the output voltage is brought into regulation any excess energy is stored on the input capacitor and its voltage increases. When a load exists at the output the buck can efficiently transfer energy stored at a high voltage to the regulated output. While energy storage at the input utilizes the high voltage at the input, the load current is limited to what the buck converter can supply. If larger loads need to be serviced the output capacitor can be sized to support a larger current for some duration. For example, a current burst could begin when PGOOD goes high and would continuously deplete the output capacitor until PGOOD went low. The output voltages available on the LTC3588-2 are particularly suited to Li-Ion and LiFePO4 batteries as well as supercapacitors for applications where energy storage at the output is desired. APPLICATIONS INFORMATION Introduction The LTC3588-2 harvests ambient vibrational energy through a piezoelectric element in its primary application. Common piezoelectric elements are PZT (lead zirconate titanate) ceramics, PVDF (polyvinylidene fluoride) polymers, or other composites. Ceramic piezoelectric elements exhibit a piezoelectric effect when the crystal structure of the ceramic is compressed and internal dipole movement produces a voltage. Polymer elements comprised of long-chain molecules produce a voltage when flexed as molecules repel each other. Ceramics are often used under direct pressure while a polymer can be flexed more PIEZO VOLTAGE INCREASING VIBRATION ENERGY readily. A wide range of piezoelectric elements are available and produce a variety of open-circuit voltages and short-circuit currents. Typically the open-circuit voltage and short-circuit currents increase with available vibrational energy as shown in Figure 4. Piezoelectric elements can be placed in series or in parallel to achieve desired open-circuit voltages. The LTC3588-2 is well-suited to a piezoelectric energy harvesting application. The 20V input protective shunt can accommodate a variety of piezoelectric elements. The low quiescent current of the LTC3588-2 enables efficient energy accumulation from piezoelectric elements which can have short-circuit currents on the order of tens of microamps. Piezoelectric elements can be obtained from manufacturers listed in Table 2. Table 2. Piezoelectric Element Manufacturers Advanced Cerametrics 0 0 PIEZO CURRENT www.advancedcerametrics.com Piezo Systems www.piezo.com Measurement Specialties www.meas-spec.com PI (Physik Instrumente) www.pi-usa.us MIDE Technology Corporation www.mide.com Morgan Technical Ceramics www.morganelectroceramics.com 35882 F04 Figure 4. Typical Piezoelectric Load Lines 10 35882fc For more information www.linear.com/LTC3588-2 LTC3588-2 APPLICATIONS INFORMATION 10µF 25V 1µF 6V PZ1 PZ2 VIN PGOOD CAP LTC3588-2 D1 D0 5V MICROPROCESSOR CORE VOUT VIN2 4.7µF 6V SW GND TX EN 22µH OUTPUT VOLTAGE 50mV/DIV AC-COUPLED GND LOAD CURRENT 25mA/DIV 47µF 6V 5mA 35882 F05a 250µs/DIV VIN = 18V L = 22µH, COUT = 47µF LOAD STEP BETWEEN 5mA and 55mA 35882 F05b Figure 5. 5V Piezoelectric Energy Harvester Powering a Microprocessor with a Wireless Transmitter and 50mA Load Step Response The LTC3588-2 will gather energy and convert it to a useable output voltage to power microprocessors, wireless sensors, and wireless transmission components. Such a wireless sensor application may require much more peak power than a piezoelectric element can produce. However, the LTC3588-2 accumulates energy over a long period of time to enable efficient use for short power bursts. For continuous operation, these bursts must occur with a low duty cycle such that the total output energy during the burst does not exceed the average source power integrated over an energy accumulation cycle. For piezoelectric inputs the time between cycles could be minutes, hours, or longer depending on the selected capacitor values and the nature of the vibration source. PGOOD Signal The PGOOD signal can be used to enable a sleeping microprocessor or other circuitry when VOUT reaches regulation, as shown in Figure 5. Typically VIN will be somewhere between the UVLO thresholds at this time and a load could only be supported by the output capacitor. Alternatively, waiting a period of time after PGOOD goes high would let the input capacitor accumulate more energy allowing load current to be maintained longer as the buck efficiently transfers that energy to the output. While active, a microprocessor may draw a small load when operating sensors, and then draw a large load to transmit data. Figure 5 shows the LTC3588-2 responding smoothly to such a load step. Input and Output Capacitor Selection The input and output capacitors should be selected based on the energy needs and load requirements of the application. In every case the VIN capacitor should be rated to withstand the highest voltage ever present at VIN. For 100mA or smaller loads, storing energy at the input takes advantage of the high voltage input since the buck can deliver 100mA average load current efficiently to the output. The input capacitor should then be sized to store enough energy to provide output power for the length of time required. This may involve using a large capacitor, letting VIN charge to a high voltage, or both. Enough energy should be stored on the input so that the buck does not reach the UVLO falling threshold which would halt energy transfer to the output. In general: ( 1 PLOAD tLOAD = ηCIN VIN 2 − VUVLO(FALLING)2 2 VUVLO(FALLING) ≤ VIN ≤ VSHUNT ) The above equation can be used to size the input capacitor to meet the power requirements of the output for an application with continuous input energy. Here η is the average efficiency of the buck converter over the input range and VIN is the input voltage when the buck begins to switch. This equation may overestimate the input capacitor necessary since load current can deplete the output capacitor all the way to the lower PGOOD threshold. It also assumes that the input source charging has a negligible 35882fc For more information www.linear.com/LTC3588-2 11 LTC3588-2 APPLICATIONS INFORMATION effect during this time. For applications where the output must reach regulation on a single UVLO cycle, the energy required to charge the output capacitor must be taken into account when sizing CIN. The duration for which the regulator sleeps depends on the load current and the size of the output capacitor. The sleep time decreases as the load current increases and/or as the output capacitor decreases. The DC sleep hysteresis window is ±16mV around the programmed output voltage. Ideally this means that the sleep time is determined by the following equation: tSLEEP = COUT 32mV ILOAD The buck is optimized to work with a 22µH inductor. Inductor values greater than 22µH may yield benefits in some applications. For example, a larger inductor will benefit high voltage applications by increasing the on-time of the PMOS switch and improving efficiency by reducing gate charge loss. Choose an inductor with a DC current rating greater than 350mA. The DCR of the inductor can have an impact on efficiency as it is a source of loss. Trade-offs between price, size, and DCR should be evaluated. Table 3 lists several inductors that work well with the LTC3588-2. Table 3. Recommended Inductors for LTC3588-2 This is true for output capacitors on the order of 100µF or larger, but as the output capacitor decreases towards 10µF delays in the internal sleep comparator along with the load current may result in the VOUT voltage slewing past the ±16mV thresholds. This will lengthen the sleep time and increase VOUT ripple. A capacitor less than 10µF is not recommended as VOUT ripple could increase to an undesirable level. If transient load currents above 100mA are required then a larger capacitor can be used at the output. This capacitor will be continuously discharged during a load condition and the capacitor can be sized for an acceptable drop in VOUT: tLOAD COUT = (ILOAD – IBUCK ) VOUT + – VOUT – Here VOUT+ is the value of VOUT when PGOOD goes high and VOUT– is the desired lower limit of VOUT. IBUCK is the average current being delivered from the buck converter, typically IPEAK /2. A standard surface mount ceramic capacitor can be used for COUT, though some applications may be better suited to a low leakage aluminum electrolytic capacitor or a supercapacitor. These capacitors can be obtained from manufacturers such as Vishay, Illinois Capacitor, AVX, or CAP-XX. 12 Inductor INDUCTOR TYPE A997AS-220M L (µH) MAX IDC (mA) MAX DCR (Ω) 22 390 0.440 4.0 × 4.0 × 1.8 SIZE in mm (L × W × H) MANUFACTURER Toko LPS5030-223MLC 22 700 0.190 4.9 × 4.9 × 3.0 Coilcraft LPS4012-473MLC 47 350 1.400 4.0 × 4.0 × 1.2 Coilcraft SLF7045T 100 500 0.250 7.0 × 7.0 × 4.8 TDK VIN2 and CAP Capacitors A 1μF capacitor should be connected between VIN and CAP and a 4.7µF capacitor should be connected between VIN2 and GND. These capacitors hold up the internal rails during buck switching and compensate the internal rail generation circuits. Additional Applications with Piezo Inputs The versatile LTC3588-2 can be used in a variety of configurations. Figure 6 shows a single piezo source powering two LTC3588-2s simultaneously, providing capability for multiple rail systems. As the piezo provides input power both VIN rails will initially come up together, but when one output starts drawing power, only its corresponding VIN will fall as the bridges of each LTC3588-2 provide isolation. Input piezo energy will then be directed to this lower voltage capacitor until both VIN rails are again equal. This configuration is expandable to any number of LTC3588-2s powered by a single piezo as long as the piezo can support the sum total of the quiescent currents from each LTC3588-2. 35882fc For more information www.linear.com/LTC3588-2 LTC3588-2 APPLICATIONS INFORMATION ADVANCED CERAMETRICS PFCB-W14 PGOOD1 PZ1 PZ2 PZ1 PZ2 PGOOD VIN VIN PGOOD 22µH 5.0V SW LTC3588-2 VOUT 10µF 6V CAP 1µF 6V 10µF 25V VIN2 D1 D0 GND 1µF 6V 4.7µF 6V 10µF 25V LTC3588-2 CAP 22µH 3.45V SW VOUT VIN2 4.7µF 6V PGOOD2 10µF 6V D1 D0 GND 35882 F06 Figure 6. Dual Rail Power Supply with Single Piezo DANGER! HIGH VOLTAGE! 150k 120VAC 60Hz 150k DANGEROUS AND LETHAL POTENTIALS ARE PRESENT IN OFFLINE CIRCUITS! 150k BEFORE PROCEEDING ANY FURTHER, THE READER IS WARNED THAT CAUTION MUST BE USED IN THE CONSTRUCTION, TESTING AND USE OF 150k 1µF 6V 10µF 25V PZ1 PZ2 VIN PGOOD CAP LTC3588-2 4.7µF 6V D0 D1 AND MAKING CONNECTIONS TO THESE CIRCUITS. REPEAT: OFFLINE PGOOD CIRCUITS CONTAIN DANGEROUS, AC LINE-CONNECTED HIGH VOLTAGE 22µH VOUT 4.1V SW VOUT VIN2 OFFLINE CIRCUITS. EXTREME CAUTION MUST BE USED IN WORKING WITH 22µF 6V GND 35882 F07 Li-Ion POWER STREAM LiR2450 120mAh POTENTIALS. USE CAUTION. ALL TESTING PERFORMED ON AN OFFLINE CIRCUIT MUST BE DONE WITH AN ISOLATION TRANSFORMER CONNECTED BETWEEN THE OFFLINE CIRCUIT’S INPUT AND THE AC LINE. USERS AND CONSTRUCTORS OF OFFLINE CIRCUITS MUST OBSERVE THIS PRECAUTION WHEN CONNECTING TEST EQUIPMENT TO THE CIRCUIT TO AVOID ELECTRIC SHOCK. REPEAT: AN ISOLATION TRANSFORMER MUST BE CONNECTED BETWEEN THE CIRCUIT INPUT AND THE AC LINE IF ANY TEST EQUIPMENT IS TO BE CONNECTED. Figure 7. AC Line Powered 4.1V Li-Ion Battery Charger Alternate Power Sources The LTC3588-2 is not limited to use with piezoelectric elements but can accommodate a wide variety of input sources depending on the type of ambient energy available. Figure 7 shows the LTC3588-2 internal bridge rectifier connected to the AC line in series with four 150k current limiting resistors. This is a high voltage application and minimum spacing between the line, neutral, and any high voltage components should be maintained per the applicable UL specification. For general off-line applications refer to UL regulation 1012. Figure 8 shows an application where copper panels are placed near a standard fluorescent room light to capacitively harvest energy from the electric field around the light. The COPPER PANEL (12" × 24") 1µF 6V 10µF 25V PANELS ARE PLACED 6" FROM 2' × 4' FLUORESCENT LIGHT FIXTURES PZ1 PZ2 VIN PGOOD CAP LTC3588-2 PGOOD 22µH 4.5V SW VOUT VIN2 4.7µF 6V COPPER PANEL (12" × 24") 10µF 6V D1 D0 GND 35882 F08 Figure 8. Electric Field Energy Harvester 35882fc For more information www.linear.com/LTC3588-2 13 LTC3588-2 APPLICATIONS INFORMATION frequency of the emission will be 120Hz for magnetic ballasts but could be higher if the light uses electronic ballast. The LTC3588-2 bridge rectifier can handle a wide range of input frequencies. Figure 9 shows the LTC3588-2 powered by a 48V communications line. In this example, 1mA is the maximum current that is allowed to be drawn. The 28k current limiting resistor sets this current as the LTC3588-2 will shunt VIN at 20V. The advantage of this scheme is that the current at the output is multiplied by the ratio of VIN to VOUT (less the loss in the buck converter). This is useful in cases where greater current is needed at the output than is available at the input. The high UVLO of 16V prevents any start-up issue as there is already a good multiplication factor at 14 that level. This same technique can be extended to AC source that also have limited current available at the input. 48V 28k PZ1 1mA 1µF 6V 47µF 25V 4.7µF 6V PZ2 VIN PGOOD LTC3588-2 22µH CAP SW VIN2 VOUT D1 D0 GND PGOOD VOUT 3.45V 3.5mA 10µF 6V + LiFePO4 35882 F09 Figure 9. Current Fed 3.45V LiFePO4 Battery Charger 35882fc For more information www.linear.com/LTC3588-2 LTC3588-2 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) 0.200 REF 5 0.75 ±0.05 0.00 – 0.05 1 (DD) DFN REV C 0310 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 35882fc For more information www.linear.com/LTC3588-2 15 LTC3588-2 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev I) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 ±0.102 (.074 ±.004) 5.10 (.201) MIN 1 0.889 ±0.127 (.035 ±.005) 1.68 ±0.102 (.066 ±.004) 0.05 REF 10 0.305 ± 0.038 (.0120 ±.0015) TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 ±0.102 (.118 ±.004) (NOTE 3) DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 10 9 8 7 6 DETAIL “A” 0° – 6° TYP 1 2 3 4 5 GAUGE PLANE 0.53 ±0.152 (.021 ±.006) DETAIL “A” 0.18 (.007) SEATING PLANE 0.86 (.034) REF 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) TYP 0.50 (.0197) BSC NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 16 0.497 ±0.076 (.0196 ±.003) REF 3.00 ±0.102 (.118 ±.004) (NOTE 4) 4.90 ±0.152 (.193 ±.006) 0.254 (.010) 0.29 REF 1.68 (.066) 3.20 – 3.45 (.126 – .136) 0.50 (.0197) BSC 1.88 (.074) 0.1016 ±0.0508 (.004 ±.002) MSOP (MSE) 0213 REV I 35882fc For more information www.linear.com/LTC3588-2 LTC3588-2 REVISION HISTORY REV DATE DESCRIPTION A 5/11 Add brackets to Absolute Maximum Ratings for VOUT and PGOOD. 2 Replace MS package description to the correct MSE package description. 15 Add to Related Parts section and order parts by part number. 16 Clarified title and Description 1 B C 7/14 8/15 PAGE NUMBER Clarified x-axis label on Figure 1 8 Clarified Figure 8 14 Clarified Related Parts list 18 Modified COUT Equation 12 35882fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representaFor more www.linear.com/LTC3588-2 tion that the interconnection of itsinformation circuits as described herein will not infringe on existing patent rights. 17 LTC3588-2 TYPICAL APPLICATION Piezoelectric Shunt Charger for Small Li-Ion Cells or Thin Film Batteries ADVANCED CERAMETRICS PFCB-W14 1µF 6.3V 22µF 25V PZ1 PZ2 VIN SW 22µH 8.87k 100µA CONTINUOUS 20mA PULSED LTC3588-2 VOUT CAP COUT 47µF 6.3V VIN2 4.7µF 6.3V VOUT 5.0V D1 D0 PGOOD GND VCC NTCBIAS 10k DMP2104LP ADJ NC7SVL04 LTC4070 NTC T* LBO GND * NTHS0805E3103LT LOCATE NEAR BATTERY 4.7M Li-ION + INFINITE POWER SOLUTIONS MEC101-10SES 4.1V 1mAh 35882 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1389 Nanopower Precision Shunt Voltage Reference 800nA Operating Current, 1.25V/2.5V/4.096V LTC1540 Nanopower Comparator with Reference 0.3µA IQ, Drives 0.01µF, Adjustable Hysteresis, 2V to 11V Input Range LT3009 3µA IQ, 20mA Low Dropout Linear Regulator Low 3µA IQ, 1.6V to 20V Range, 20mA Output Current LTC3105 400mA Step-Up Converter with 250mV Start-Up and Maximum Power Point Control High Efficiency Step-Up DC/DC Converter, VIN: 0.225V to 5V, Integrated Maximum Power Point Controller (MPPT), Photovoltaic Cells, Thermoelectric Generators (TEGs), and Fuel Cells, Burst Mode® Operation LTC3108/ LTC3108-1 Ultralow Voltage Step-Up Converter and Power Manager VIN: 0.02V to 1V, VOUT = 2.2V, 2.35V, 3.3V, 4.1V, 5V, IQ = 6µA, 4mm × 3mm DFN-12, SSOP-16 Packages, LTC3108-1 VOUT = 2.2V, 2.5V, 3V, 3.7V, 4.5V LTC3109 Auto-Polarity, Ultralow Voltage Step-Up Converter and Power |VIN|: 0.03V to 1V, VOUT = 2.2V, 2.35V, 3.3V, 4.1V, 5V, IQ = 7µA, 4mm × 4mm QFN-20, SSOP-20 Packages Manager LTC3388-1/ LTC3388-3 20V High Efficiency Nanopower Step-Down Regulator 860nA IQ in Sleep, 2.7V to 20V Input, VOUT: 1.2V to 5V, Enable and Standby Pins LTC3588-1 Nanopower Energy Harvesting Power Supply 950nA IQ in Sleep, VOUT: 1.8V, 2.5V, 3.3V, 3.6V, Integrated Bridge Rectifier LTC3631 45V, 100mA, Synchronous Step-Down Regulator with 12µA IQ 4.5V to 45V Operating Range, Overvoltage Lockout Up to 60V LTC3642 45V, 50mA, Synchronous Step-Down Regulator with 12µA IQ 4.5V to 45V Operating Range, Overvoltage Lockout Up to 60V LT3652 Power Tracking 2A Battery Charger for Solar Power MPPT for Solar Applications, VIN: 4.95V to 32V, Charge Rate Up to 2A, User Selectable Termination: C/10 or On-Board Timer, Resister Programmable Float Voltage up to 14.4V, 3mm × 3mm DFN12 or MSOP-12 LT3970 40V, 350mA Step-Down Regulator with 2.5µA IQ Integrated Boost and Catch Diodes, 4.2V to 40V Operating Range LT3971 38V, 1.2A, 2MHz Step-Down Regulator with 2.8µA IQ 4.3V to 38V Operating Range, Low Ripple Burst Mode Operation LT3991 55V, 1.2A 2MHz Step-Down Regulator with 2.8µA IQ 4.3V to 55V Operating Range, Low Ripple Burst Mode Operation LTC4070 Li-Ion/Polymer Shunt Battery Charger System 450nA IQ, 1% Float Voltage Accuracy, 50mA Shunt Current 4V/4.1V/4.2V LTC4071 Li-Ion/Polymer Shunt Battery Charger System with Low Battery Disconnect 550nA IQ, 1% Float Voltage Accuracy, <10nA Low Battery Disconnect, 4V/4.1V/4.2V, 8-Lead 2mm × 3mm DFN and MSOP Packages LTC3330 Nanopower Buck-Boost DC/DC with Energy Harvesting Battery Life Extender VIN: 2.7V to 20V, BAT: 1.8V to 5.5V, 750nA IQ, 5mm × 5mm QFN-32 Package LTC3331 Nanopower Buck-Boost DC/DC with Energy Harvesting Battery Charger VIN: 2.7V to 20V, BAT: Up to 4.2V, Shunt Charger, Low Battery Disconnect, 950nA IQ, 5mm × 5mm QFN-32 Package 18 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 For more information www.linear.com/LTC3588-2 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LTC3588-2 35882fc LT 0815 REV C • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 2010